Why do police devote time to ticketing cyclists who jump red lights? The obvious answer is: because they're breaking the law. But of course it's more complex than that.

Every police force has to prioritise. Given, some cyclists ask, that of the 600 or so pedestrians killed in the UK each year, about one on average is struck by a bike, why bother? Why not devote the resources to real traffic dangers like light-jumping cars and trucks?

I got a chance to put this to the police force at the very front line of urban cycling in the UK. Ever more bike commuters flock to and from London's City district every day, their numbers swelled by couriers flitting between the banks and law firms.

City police are known for being particularly active in targeting cyclists. In fact, many London riders see the force as decidedly anti-bike, a curious paradox given that it has the country's only dedicated cycling police unit.

Earlier this week, as the force's cycle team took me through its training course, I got the chance to meet Superintendent Lorraine Cussen, in overall charge of the Snow Hill police station and thus the bike squad based there. "I don't think we're anti-cyclist. A couple of years ago we could perhaps have been accused of that, but things have changed," she told me.

Why, then, do I see so many City officers pulling over cyclists? The main answer, it seems, is public demand.

Police forces are now obliged by central government to tackle issues flagged up by local communities. In the City, this tends to bring complaints about rough sleepers and law-flouting cyclists.

"When we ask the community what they want us to do, cycling comes up again and again," Cussen says. "It's the same in other police areas – when people are asked what they're most concerned about it's often anti-social behaviour rather than more serious crimes."

Recent statistics from these demand-led operations show that officers also pull over miscreant drivers (pedestrians who sprint suicidally into traffic are not breaking any laws, so can only be warned). But this doesn't mean they're less worried about the red light-allergic cyclists.

PC James Aveling, a City bike patrol officer for nine years, argues that it's a bigger problem than the accident statistics suggest. For one thing, he says, there is no legal obligation to report collisions between bikes and pedestrians, so many never reach the statistics books. He and his colleagues also deal with more and more angry confrontations between cyclists and pedestrians.

With more than 800 officers and just over one square mile of streets to patrol, the force can make a real difference, he says: "We're never going to stop it completely, but we want to try and improve behaviour. There's what we call the lemming effect – if one cyclist crosses on a red, others tend to follow. If it's a courier doing it they maybe know what they're doing, but lots of others simply don't."

Aveling also filled me in on another great cyclist mystery: why do police sometimes seem lax on drivers and motorcyclists who stray into bike lanes and bike-only advance stop zones (ASZs)?

The bike lane question is simple: if it is bounded by a dotted line rather than a continuous one then it is purely advisory, meaning it has no legal status. "Some councils paint the lanes green," Aveling adds. "That doesn't mean anything either."

As for the ASZs, the issue is decidedly murky: they are usually bounded by a continuous white line except for a small gap on the kerb-side edge, which is the only legal way to enter them. Even as a cyclist you're officially committing and offence if you enter the ASZ from the centre or right, I'm told.

Booking cars which enter the zone is tricky, Aveling says, as it's not illegal if they stop in one if a light turns red as they're part-way in. Officers thus have to watch a driver creep in on an already red light. There are also rumours that some officers see the penalty for the infringement – six points on the licence the same as you'd get for sailing all the way through the red light – as a somewhat dispoportionate.

More generally, Aveling is sceptical about ASZs, believing they suit experienced cyclists but not beginners, who might be better off sitting behind waiting traffic rather than pushing through.

He's far too polite to say so, but I get the distinct impression that overall, he's not too impressed with a lot of the cycling infrastructure on UK roads. That makes two of us.